During your career as a pilot you will see more advanced navigation systems in the airplanes you fly. Systems like Radio Magnetic Indicators, Horizontal Situation Indicators and navigation systems like RNAV, LORAN (now obsolete) and satellite navigation systems as GPS.

We will touch the surfaces on each of these systems and discuss how they work basically. As each manufacturer creates his own system it is almost impossible to discuss every system in depth on the market today.

Advanced Navigation Indicators

The RMI, Radio Magnetic Indicator, is a combination of the directional gyro (heading indicator) with two bearing pointers. The double needle is the ADF/NDB and the single needle is the VOR or sometimes another ADF, depending on configuration. Usually the RMI compass card is a slaved one referenced to magnetic north.

A HSI, Horizontal Situation Indicator, combines a heading indicator with a VOR indicator with deviation dots in one display. Included is also a glide slope indicator for ILS approaches and a TO/FROM flag.

The advantage of these indicators is a very high situational/navigational awareness regarding your position.

Area Navigation RNAV

RNAV Navigation

RNAV is a system that uses a VOR/DME or a VORTAC (VOR and Military TACAN) in combination with a course line computer (CLC). This CLC is able to create phantom VORs, it relocates the VOR from the original position in such a way that this phantom VOR becomes a way point along your route. This makes it possible to fly in a straigth line, ie following (zigzagging) VORs, to your destination. See picture to the right.

An advantage of RNAV is that you can navigate with the VOR indicator. Needle deflection indicate course corrections but the deviation scale (dots) is in nautical miles ie degrees. The DME part will show the correct distance to the way point, ground speed can differ. That depends on what the manufacturer of the CLC has set, just read the manuals.

RNAV provides course and distance information and gives you the ability to fly direct routes thereby saving fuel and time lowering your aircraft expenses.

Area Navigation LORAN-C

LORAN-C is a LOnge RAnge Navigation system type C. It is based on a number of worldwide located high power LF (90 - 110 KHz) stations transmitting a set of coded pulses from a master station and a secondary station transmitting after the master pulse.

LORANs future is quite uncertain as GPS is taking over as navigation system. Personally I think it would be a good backup to satellite based navigation as LORAN signals are strong and difficult jam. To learn more about read LORAN technical details for a good article about LORAN in Wikipedia.

The US Coast Guard Navigation Center, which operates LORAN, has a website dedicated to this system.

Area Navigation GPS

GPS, Global Positioning System, is a space/satellite based navigation system, in contrary to LORAN and RNAV which are terrestial based. It provides highly accurate time, positioning and speed information to its unlimited users. The system is online 24/7/365 and not affect by weather whereas LORAN and VORs can be. Its navigation is based on a worldwide grid reference system, constant knowledge of the spatial position of the satellites and a very accurate time system.

The GPS receiver has a number of channels (8 - 12) to receive and track satellites in its view. The satellites orbit the earth in 90 minutes and there are at least 24 satellites active/online. These signals are (with triangulation) translated into a two or three dimensional position fix (three sats, with four it can calculate altitude). Accuracy for civil users is around 328 feet/100 meters, although this is improving. Military users have a much higher accuracy. For more in depth GPS technical information we refer you to Wikipedia.

GPS started as backup to VFR navigation (although some users used it as primary system then) and has evolved into an IFR certified navigation system serving navigation enroute and approaches to runways.